December's ENSO Update: Close, but no cigar.

The first Thursday of every month is when we do the CPC/IRI ENSO status update, when NOAA officially answers the question “Are we there yet?” This month, the answer is...close, but no cigar.

Sea surface temperatures (SSTs) in the Niño3.4 region of the Pacific were quite warm during November, with the most recent weekly Niño3.4 index value at +1.0°C above average. The threshold for El Niño conditions is +0.5° above average for one month, and most of the climate models are forecasting that SSTs will stay above average for at least a few more months. Then why haven’t we changed from an “El Niño Watch” (favorable for development of El Niño conditions) to an “El Niño Advisory” (El Niño conditions are present)?

The atmosphere just won’t get with the program

First, a quick review of what we mean by “El Niño conditions.” There are three components:

(1) A one-month SST anomaly of +0.5°C or greater in the Niño3.4 region (check!),

(2) An expectation that the warm SSTs will meet or exceed that threshold for the next few months (seems very likely!),

In a nutshell, the typical El Niño atmospheric response includes reduced rainfall over Indonesia, more rainfall over the central Pacific, and some weakening of the low-level easterly winds and upper-level westerly winds (the Walker circulation) along the equator. As of the beginning of this month, we have seen reduced Indonesian rainfall, but we have not seen more rain over the central Pacific (the opposite, in fact), and changes in the Walker circulation are unclear.

The most common way of looking at the rainfall patterns in the tropics is to use outgoing longwave radiation, which is monitored by satellites. Solar energy reaches Earth as shortwave radiation, is absorbed by the surface, and heats it up. The warmed surface then radiates longer-wavelength energy back out to space. This outgoing longwave radiation (OLR) is intercepted by clouds, so when the satellites see less OLR than average in a location, it was probably cloudier—and in the tropics, that means rainier—than usual there. And vice versa: more OLR means fewer tropical clouds and less rainfall.

Can we get a little more rain over here?

Figure 2 shows the average November OLR anomaly over the tropical Pacific. That big orange spot near the Date Line means higher OLR than average: fewer clouds and less rainfall. With El Niño conditions, we’d normally expect more rain than usual in this region, so the decreased rain tells forecasters that the atmosphere may not be adequately coupled to the warm SSTs yet. The presence of convection (storminess) in this region matters so much because this is how El Niño communicates between the equatorial Pacific and the higher latitudes, kicking off a cascade of global impacts.

Figure 2: Outgoing longwave radiation (OLR) departure from average for November 2014. Map by Emily Becker and Fiona Martin.

Another measurement also suggests we’re not quite in El Niño conditions: The Southern Oscillation Index (SOI; the surface pressure anomaly difference between Tahiti and Darwin, Australia) is in negative territory (-0.9), but the Equatorial SOI, which compares the pressure anomalies between the western and eastern equatorial Pacific, is near zero. With El Niño, we’d expect to see negative SOI, because that indicates a weakening of the Walker Circulation.

On the other hand, there is some orange over Indonesia in Figure 2, meaning fewer clouds and reduced rainfall, which is compatible with El Niño conditions. As well, November upper-level westerly winds and lower-level easterly winds were both slightly weaker than average. The atmosphere may be beginning to respond, but not convincingly enough for forecasters to declare an El Niño Advisory.

For some El Niño impacts, “close” is close enough

El Niño impacts can emerge in different parts of the globe, even if the NOAA definition hasn’t yet been formally satisfied. Different countries have different thresholds for El Niño, which are tailored to their specific interests.

For example, the Peruvian National Committee on El Niño Studies (ENFEN) declared a “moderate coastal El Niño” in May of this year; SST anomaly in the easternmost Niño1+2 region is the primary metric for their declaration of coastal El Niño. Their event peaked in July, and is still ongoing. Atmospheric coupling is not required for them to see impacts: the strong downwelling Kelvin wave in the spring and associated warm SSTs near the Peruvian coast reduced the spatial distribution of anchovies, an important fishery for Peru.

What next?

Recently, the observed increase in SST anomalies has generally matched up well with forecasts from most climate models. The August, September, and October forecasts from the NMME predicted a November Niño3.4 SST anomaly between +0.7°C and +0.9°C. Due to the recent warming and our expectation that ocean temperatures will continue to be above-average, forecasters this month have again increased the odds of El Niño this winter to an approximately 2-in-3 chance.

A blog about monitoring and forecasting El Niño, La Niña, and its impacts.

Disclaimer:

The ENSO blog is written, edited, and moderated by Michelle L’Heureux (NOAA Climate Prediction Center), Emily Becker and Tom Di Liberto (contractors to CPC), Nat Johnson (NOAA Geophysical Fluid Dynamics Laboratory), and Rebecca Lindsey (contractor to NOAA Climate Program Office), with periodic guest contributors. Ideas and explanations found in these posts should be attributed to the ENSO blog team, and not to NOAA (the agency) itself.

Comments

Thank you so much for this information. I really wish I knew how to read "all the things" well enough to be able to adjust my own forecast. Once a month is killing me, the anticipation >.<. So, I view all the charts, do a lot of googling to figure out how to read them and come to my own conclusions. I witnessed the Ice Storm of '98 in the Northeast as a child and it's one of those events you don't really forget. I know it was a very bad and costly event ( up here and the whole el nino impact globally ), but an exciting one at the same time. How many people hear acres of trees cracking around them because the ice is that heavy and that thick? We had no power for weeks! The woods are still scarred.

We don't get a lot of exciting weather up in these parts ( even out snow and t-storms seemed to have gradually moved south ) so I like to keep an eye on things. Cali is getting some rain though and we have had a smidgen of freezing rain and mild temperatures ( in between the frigid ones lol ) so maybe there is a mild effect. I believe this el nino is located in a different spot than in 98 though so the impacts aren't as clear to me. I know nothing about any of this, just a weather enthusiast learning what I can from the web and the noaa/nws sites. Pardon the long comment but I'm pretty much the only person I know interested in this :)

I moved my 90-day winter trip on Montana and Idaho’s portion of the Continental Divide to an earlier date. The reason is the possible El Niño event. By the next ENSO update on January 8, I will probably already be in the backcountry, one month early. With 460 miles in front of me and the Anaconda-Pintler Wilderness being most of the last 110 miles, an El Niño event could play havoc on that final month of travel, if I am traveling in the latter part of April.
There is also a risk by leaving so early. However, I am unable to wait for that next report. Instead I will rely on what I see going on through the month of December. And yes, I will continue to watch the NOAA forecasts, including the 3-month extended forecast.

So we have a Semi El Nino. That's cool. But what about the gigantic swath of ocean directly upstream from California (my home) and the continental US which is currently 2-4 degrees C above normal? To me, this seems like it would play a pretty big part in our winter season as low pressure systems drop down over it, then over us, and churn out rain.
Current:http://www.ospo.noaa.gov/data/sst/anomaly/2014/anomp.12.4.2014.gif

IT is unfortunate that when the entire Equatorial Pacific Ocean has warm anomaly now., Your entire spot light is the long term average temperature anomaly of Nino 3.4 region only. Ultimately any selected region in the Pacific Ocean is simply “line drawn on water surface” and seems to me meaningless. Please see one your own figure from at another site given .below.

You're right that one region in the Pacific can have different results from another region. The Nino3.4 region has historically had the highest correlation with the ENSO-related changes in atmospheric circulation that we're interested in, so that's why we use that as our primary index.

The southeastern half of Maryland does have a slightly increased chance of more precipitation than average... but snow is very hard to predict. This is especially so in Maryland, where the winter temperature can hover right around freezing, and a degree or two can make the difference between a rainy day and a snowstorm.

It sure seems like El Nino conditions have arrived here--to remain for the foreseeable future. After a cold November we are now stuck with persistent overcast conditions, mild weather (near-freezing daytime highs), and only a few inches of snow on the ground.

This is in stark contrast with last winter, which brought 148 inches of snowfall (that lasted into May), and 83 sub-zero nights.

While EN is important, I am wondering if we are seeing more then a "Temporary shift" in the semi permanent upper air patters, which of course leads to the discussion on warmer oceans directing u/s or is u/s directing new oceans changes as well as the impact of warming on the oceans. It seems, and much to early to know for sure, but seems that U/A patterns are slightly shifting from their previous semi permanent location. and they are heavily impacted by warming and moisture transports. EN as you say "may or may not" be doing something, but I am starting to wonder if the U/A shifting are having bigger impact as oceans heat up? Just an obs, as do not have the resources to look at such things, but seems suspicious with warming going on over shall we say "7/8th of earth
/

I'm new to group so have a lot of catchup reading to do. One possibly premature observation. Many posting here seem to still be looking for linear change if any at all while acknowledging climate change. An El Niño event may well be nearly unrecognizeable and still manifest in some basic recognizeable elements. Perhaps.

I and others were hoping for an El Nino--instead we have had nearly 15 inches of rain since October 1 in the Portland, Oregon area.
Coupled with high winds, and significantly fluctuating temperatures, it has been a wet and chaotic fall. Ready for this rain to move south to California where they need it.